Jet perforator for well casings



Feb. 6, 1962 E. D. EDWARDS ETAL 3,019,731

JET PERFORATOR FOR WELL CASINGS Original Filed Dec. 21,1956

INVENTORS w r W dh 5 MM Mm MW E pin! ATTORNEYS sprain Patented Feb. 6,1952 3,019,731 JET PERFORATOR FOR WELL CASHJGS Edwin David Edwards,Wichita Falls, and Ralph J. Hach,

Plano, Ten, assignors to Advanced Gil Tools, inc, Wichita Falls, Tex., acorporation of Delaware Continuation of application Ser. No. 629,836,Dec. 21,

1956. This application Feb. 19, 1950, Ser. No. 9,652

8 filaims. (Cl. 192-420) I This invention relates to new and usefulimprovements in jet perforators for well casings.

The invention is particularly concerned with jet perforating guns whichcut an elongate vertical slot in the well pipe or casing rather than thesubstantially circular opening now obtained by conventional jetperforating guns.

It is conventional practice to employ shaped charges, utilizing theMonroe effect, for the perforating of well casing or pipe when it isdesired to open one or more lends itself to efiicient use in well pipesof varying diameters, in which the necessary manufacturing tolerancesfor the charge may be achieved with consistency, and by passageways fromthe interior of the pipe into the earth formation. Thus, it iswell-known to drill a well bore through at producing formation, andafter the well casing or casings have been set or cemented in position,to perforate through the casings and cement into the producing formationso that the desiredpetroleum products, such as crude oil, may flow fromthe formation into the well pipe for recovery. Obviously, the size ordiameter of the perforation is limited in that the well casing must notbe too greatly weakened, and the larger the cross-sectional area of acircular perforation, the greater the extent to which the pipe isdiminished in strength. Further, the closeness of spacing of theperforations is limited in that each perforation requires an explosivecharge of a certain minimum weight, and the aggregate weight of thevarious explosive charges, all of which are exploded substantiallysimultaneously, is subject to a very definite maximum value. Thus, nomore than a certain gross weight of explosive must be detonated within-awell bore at one time for fear of excessive damage to the well pipe, ormore importantly, excessive damage to the layer or layers of cement inwhich the pipe is set.

In view of the foregoing, it is apparent that a vertical slot in thepipe is desirable in that greater flow areas, or flow passages ofgreater cross-sectional area, are provided without excessive weakeningof the pipe or casing. Further, the larger flow area obtained permitsthe utilization of fewer charges or shots, and the permissible maximumgross weight of explosive which may be detonated at one time in a wellbore, is not so quickly approached.

It is, therefore, one object of this invention to provide an improvedjet perforator for well bores utilizing a shaped charge which willproduce a vertical slot in the well pipe and extending into the earthformation.

A further object of the invention is to provide an improved jetperforator for well pipe in which a slot-cutting, shaped charge iscontained in a cylindrical housing whereby compact and closely-spacedhousings may be employed for any desired vertical spacing of the slotscut in the well pipe, and further, whereby the longitudinal axis of theslot may be varied at will if such variation is found desirable ornecessary.

Yet another object of the invention is to provide an improved jetperforator for well pipes in which a charge and acharge housing ofcertain proportions and dimensions means of which a slot of the generalshape of an elongate, narrow, ellipse is cut in the well pipe.

A construction designed to carry out the invention will be hereinafterdescribed, together with other features of the invention. 7

The invention will 'be' more readily understood from a reading of thefollowing specification and by reference to the accompanying drawing,wherein an example of the invention is shown, and wherein:

FIG. 1 is a view in elevation illustrating a well perforating gunconstructed in accordance with this invention and adapted forutilization of jet perforating charges constructed in accordance withthis invention,

FIG. 2 is an enlarged, vertical, sectional view taken upon the line 22of FIG. 1, the plug or rearward portion of the charge housi-ngbeingrotated slightly to illustrate the mounting of the firing cord thereon,

FIG. 3 is a horizontal, cross-sectional view taken upon the line 33 ofFIG. 2,

FIG. 4 isa view in perspectivepf the charge,

FIG. 5 is a vertical, cross-sectional view illustrating the general typeof perforation obtained by this charge, and

FIG. 6 is a view in elevation illustrating the shape of the slot cut bythis charge in the well pipe.

This application is .a continuation of our co-pending application,Serial No. 629,836, filed December 21, 1956, now abandoned. V

In the drawings, the numeral 10 designates a conventional perforatinggun cable of the well-known type including strands of steel wire forsupport purposes, and a pair of electrical conductors 11 for supplyingan electrical firing current to the perforating gun. The lower end ofthe cable is secured in a rope socket 12 carrying a gun head 13 to whichis connected, a firing mechanism 14 containing the conventional firingcharge or cap which is adapted to be detonated electrically. Thisgeneral assembly and type of structure is well-known-in the art and con?ventional in nature.

A supporting tube 15 depends from the lower portion of the element 14and carries one or more jet perforating assemblies 16. The tube 15 isdesirably lightweight in nature and functions to space theself-destroying assemblies 16 from the head assembly 13 and 14 so thatthe latter maybe withdrawn from the well bore without having undergoneappreciable damage when the several charges are fired. Lightweightaluminum tubing has been found quite suitable for fabrication of thetube 15. As will be explained more fully hereinafter, each of the jetperforation assemblies 16 receives an explosive cord 17 leading from aconventional detonating cap (not shown) carried within the body 14 andadapted, to be fired electrically. The cord 17 may be the widely knownPrima Cord, a commercially available product in widespread use fordelivering an explosive force to a number of spaced points, or anysuitable explosive cord of the well-known types which contain detonatingexplosives which generate very high velocity explosive waves or forces.Examples of such explosives are pentaerythritol-tetranitrate, known asPETN, Tetryl, Pentolite, composed of PETN'and TNT, Trinitrotoluene,known as TNT, Amatol, Cyclonite, RDX, Tetrytol,'composed of Tetryl andTNT, and other acre 731 explosives, all of which are well-known and arecommercialy available. Upon the supplying of an electrical firingcurrent through the conductors 11, the'detonating cap is exploded in theusual fashion and in turn, detonates the firing cord 17 which almostinstantaneously conducts an explosive force or wave to each of theassemblies 16, resulting in detonation of the latter.

' The jetperforator assemblies 16 include a cylindrical housing 18having one end closed by an integral, dished head 19, and the other endopen to receive a closure or sealing plug 20. A tubular collar or boss21 extends radially'upwardly from the upper wall of the housing 18, anda similar, tubular collar or boss 22 extends radially downwardly fromthe lower Wall of the housing. The outside diameter of one of the bosses21 and 22 is of such magnitude to permit it to slip within the other orlarger boss of a similar jet charge housing, in the particularembodiment illustrated in the drawings, the lower boss 22 being of suchoutside diameter as to slip readily within the upper boss 21. Each ofthe bosses is provided with a plurality of radially-extending openings23, such as the four equally-spaced openings shown in the drawings,whereby when the bosses are telescoped with one another, a cotter pin orkey 24 may be passed through the alined openings of the two bosses tojoin two of the housings 18 together. Theprovision of a plurality of theopenings 23 permits rotational adjustment of successive charge housingsso that all the charges may fire in one direction, each successivecharge may fire in a direction displaced 90 from the charge thereabove,or 180 from the charge thereabove, or any other suitable or desirablearrangement. In most instances, each succeeding charge will be displaced90 from the charge thereabove so as to obtain a uniform and properlyspaced pattern of perforations.

Each of the housings 18 is provided with a cylindrical bore 25 withinwhich the cylindrical charge 26 has a snug sliding fit, and terminatesadjacent the head 19 in a shoulder 27 against which the charge may seat.The inner wall-of the head 19 is, of course, dished to conform to theconvex outer wall of, the head and be spaced from the explosive charge.The cap 20 has an annulus 28 cut awayon its inner face and near itsperiphery to form a marginal flange 29 which has a press fit in theouter end of the bore 25. In addition, a flange 30 'is provided on thecap 20 for abutting the open end of the housing 18, and the latter maybe chamfered, as shown at 31, so as to receive a sealing O-ring 32 whichis distorted by the flange 30 into Sealing position and thus assureswatertight integrity for the interior of the housings 18.

The cap 20 also is provided with a central recess 33 on its inner facefor receivin'ga booster charge 34, the recess 33 extending very closelyto the outer face of the .cap 20 so that only a very thin wall 35 ispresent between the booster charge 34 and the firing cord 17. As shownin FIG. 1, the firing cord is spiraled around the assembly ofperforating charges approximately in a helix, a portion of the cordpassing over the center portion of each of the caps 20 and being held insnug engagement with the end wall section 35 by means of an overlyingclip 36. Thus, when the firing cord 17 is detonated, its'explosive waveor force will almost instantaneously perforate or burn through the thinwall section 35 for substantially simultaneous detonation of all of thebooster charges 34.

These jet perforation assemblies 16 are of the selfdestroying type anddesirably are formed of a suitable cast aluminum alloy, or other of thevarious well-known alloys which are readily drillable, will readilybreak or fracture under explosive forces, and which need have onlysufficient strength as to withstand the hydrostatic head or pressure towhich they are subjected in the well bore. The housing 18 can berelatively thin Walled in nature, and the plugs 20, likewise, need onlybe of sufficient massiveness as to insure proper assembly of the 4, pperforating structure and water-tightness thereof. To aid in thedisintegration, or possible subsequent drilling up of the plugs 20, theymay be weakened by a plurality of recesses 37 formed in the outer facesof the plugs.

The explosive charges 26 are desirably housed in a thin-walled metallicshell or tube 38 for ease in handling and positioning within the bores25 of the housings 18. Insofar as the perforating results which areobtained, however, the shell 38 is of little importance except that itmust be of such nature as to fracture or break up readily uponoccurrence of the explosion, and any fragments which remain should bereadily drillable from the well bore. The rearward portion of the sleeve38 is filled with a suitable explosive material 39, to be discussedhereinafter, which extends forwardly against a liner 40 of V-shapedcross-section. As shown in FIGS. 3 and 4, the .liner is relatively thinand has its apex 41 directed rearwardly toward the plug 20 when it ispositioned within the housing 18. Each leaf or wing 42 of the liner issemi-elliptical in form, the two wings joining at an angle ofapproximately 90, and the semielliptical shape of the wings resulting inthe entire perimeter or periphery of the liner engaging the inner wallof the shell 38. Thus, the liner completely encloses the forward portionof the explosive charge 39, and the forwardmost edges 43 of the linerterminate at or near the forwardmost edge of the shell 38 which, aspreviously pointed out, abutsthe shoulder 27. The rearward face or partof each of the charges 26 is flat so as to be snugly abutted by theinner face of the plugs 20, the flanges 29 engaging the rearward edge ofthe sleeves 38 to hold the same in snug engagementwith the shoulders 27,and

the recesses 33, containing the booster charges 34, being brought intocontiguity with the rearward face of the explosive charge 39. Thus, thedetonation of the booster.

charges 34 results in the virtually instantaneous detonation of the jetperforation charges 39.

A jet perforator charge of the configuration illustrated and describedwill cut a slot in a well pipe rather than a circular opening, such ashas been conventional practice, and the general outline of a typicalperforation obtained by this charge is shown in FIGS. 5 and 6. Thecharge assembly 16 is indicated in dotted lines in FIG. 5, and as shown,a slot 44 will be cut through the inner casing 45, the cement orconcrete bedding 46 for the casing, the second well pipe or casing 47,and into the formation 48. As shown in FIG. 6, the slot 44 is of thegeneral shape of a flattened ellipse, a typical penetration for a charge2 inches in diameter being the formation of a slot. approximately 3inches long and of an inch wide at its widest point. Necessarily, theslot will decrease in length and Width as it is traced into theformation, the slot formed in the second pipe or casing 47 inthe aboveinstance being approximately 2 inches long and /2 inch wide at itswidest point. For best results, it is, of course, important that theperforator assemblies 16 be spaced slightly from the Well pipe, the mostdesirable spacing having been found to be from /2 to 1 inch diameter ofthe charge 26, this, in the case of a 2 inch diameter charge, being from'1 to 2 inches. This spacing is not critical or absolutelyessential, butin general, is obtained without difliculty and more or lessautomatically when a shot assembly string, as illustrated in FIG. 1, islowered into a well casing which is of somewhat larger diameter thansaid' assembly.

The charge illustrated will cut a slot having its longitudinal axisalined with the apex 41 of the liner 40, and

. due to the cylindrical configuration of the charge 26,

it is obvious that longitudinal axis of the resulting slot may beoriented in anydesired direction. In most instances, it is preferredthatthe slots be cut parallel to the longitudinal axis of the well pipe, butvarious degrees of angularity are readily obtained simply by revolvingthe charges 26 within the housings 18, or slots at a varying number ofangles may be obtained by suitable revolving of the individual chargeswithin the individual housings 13. Further, it is to be noted that thedetonation of the charge 39 is instituted in the geometrical center ofthe rearward portion of the charge and in alinement with the apex 41.This is important for obtaining uniform and proper detonation and formaintaining the desired degree of directionality of the resulting,slot-cutting jet.

The booster charges 34 and the jet forming charges 39 may be formed ofany suitable or desirable explosive material, such as those enumeratedhereinabove for use in the firing cords 17. In general, of course, thebooster charge is formed of an explosive more sensitive to shock thanthe charge 39, and more readily capable of being detonated by the firingcord 17, and in turn, to function to detonate the main charge 39.

A charge 2 inches in diameter has been found most suitable for generaloil field use in that satisfactory perforation of the well casing isobtained, and such a charge is quite capable of handling the varioussizes of casings most commonly encountered. The charge should consist offrom 50 to 100 grams of explosive compacted under pressure within thesleeve 33 to a specific gravity of 1.5 to 1.6. An acceptable slot isobtained when 50 grams of explosive is employed, but it is preferred toemploy 65 to 75 grams of explosive in order to obtain a relativelynarrow and quite deep slot and perforation. Above 75 to 100 grams ofexplosive does not produce any appreciable increase in the depth ofpenetration, but does add to the total quantity of explosive beingdetonated in the Well bore and hence becomes objectionable. Since all ofthe perforating charges detonate substantially simultaneously, theircombined weights of explosive must be considered as the quantity ofexplosive being discharged, and this value must be kept below certainlimits in order to avoid damage to the well pipe or to the cement inwhich it is embedded. Accordingly, it may be stated that the charge ineach of the assemblies 16 should not exceed 75 to 100 grams nor be lessthan 65 to 70 grams. As before stated 65 to 75 grams of explosiveproduces optimum results and is much to be preferred. Similarly,although the explosive may be compacted to a specific gravity of 1.5, agravity of 1.6 is preferred and results in better performance andpenetration by the charges.

The diameter of the shells 38 and hence, of the charges 26, necessarilybecomes critical in conjunction with the weights of explosive chargesgiven hereinabove. The charge diameter should be from 1% inches to 2%inches for consistent obtaining of a 3 inch slot in the pipe 45, itbeing pointed out that smaller diameter charges do not have theuniversal adaptability and application of a charge of the sizespecified, and larger charges tend to involve too much explosive and tocut a slot of too great width. This, then, is an instance in which thedimension of the charge as Well as its configuration becomes of importance.

The liner 40 may be formed of Zinc, tin, aluminum, or nickel, butpreferably and most desirably is formed of copper or brass. The liner4%) must be between 0.040 and 0.080 of an inch thick, with 0.055 to0.065 of an inch being preferred and furnishing the best penetrationresults. Below 0.040 of an inch, sufficient penetration is not alwaysobtained, and the slot tends to become wider. Above 0.080 of an inchthickness for the liner 40, penetration also starts to diminish and theslot 44 may narrow excessively. Thus, the liner preferably is formed ofcopper or brass and must be between 0.040 and 0.080 of an inch thick.

The angularity of the apex 41, or the included angle between the faces42, is also critical and must be from 85 to 95 90 is preferred, but asmuch as 5 variation may be tolerated without excessive loss ofperformance. It is also essential that the apex 41 be properly centeredor alined with the central axis of the charge 39, Y

the maximum tolerance of misalinement being 0.015 of an inch. As thinnerliners are used, such as liners of 0.040 of an inch thick, thecriticality of misalinement becomes more pronounced and should notexceed a maximum of 0.010 of an inch.

The jet perforating assembly which has been shown and described isinexpensive to manufacture and assemble, and readily lends itself towidely varying conditions of use in the cutting of slots in the walls ofa well pipe at any suitable or desired angle. The structure is ofsufficient strength and watertight integrity as to withstand thehydrostatic pressure encountered under operational conditions, but, atthe same time, is of such nature as to be virtually self-destroying, anyfragments of a detonating assembly remaining in the Well being readilydrillable from the Well bore with conventional equipment. The variouslimitations and dimensions which have been recited were determinedempirically since no method of calculation of these critical factors andlimits is known to exist.

The combination of a cylindrical charge having an angular liner andcavity is unique and permits wide variation in the operation of the gunalthough in most instances, it will be desired to cut slots in a wellpipe parallel to the axis of the pipe. Further, the specific ranges ofweights, dimensions, density, alinement, thicknesses, and angles, whichhave been enumerated, have all been found critical and important foreffective operation of the charges, and it has been established thatvariation outside of those ranges and limits which have been givenresult in unsatisfactory performance and an unreliable jet perforatingcharge.

The foregoing description of the invention is explanatory thereof andvarious changes in the size, shape and materials, as well as in thedetails of the illustrated construction may be made, within the scope ofthe appended claims, without departing from the spirit of the invention.

What we claim and desire to secure by Letters Patent is:

1. A jet perforating charge for well pipe comprising a cylindrical bodyof an explosive having a recess defined by two plane faces at one endthereof With the recess faces forming a dihedral angle, with the apexline of the dihedral angle substantially intersecting the central axisof said body at right angles thereto, a detonator at the end of saidbody opposite said recess and aligned with the body central axis, and ahousing containing the body of explosive.

2. A jet perforating charge as set forth in claim 1, and a metallicliner in the recess and conforming thereto.

3. A jet perforating charge as set forth in claim 2 wherein saiddihedral angle is within the range of to 4. A jet perforating charge asset forth in claim 3 wherein the thickness of said liner is within therange of 0.04 to 0.08 inch.

5. A jet perforating charge for well pipe comprising a body of anexplosive having a central longitudinal axis, a front face, and a rearface, with said front face having a recess defined by two plane facesforming in said body a dihedral angle, with the line of the dihedralangle apex perpendicular to and substantially intersecting said centralaxis, and with each said plane face having the shape of a minor segmentof an ellipse with the axis of symmetry of said segment normal to andbisecting said apex line, a detonator adjacent the rear face of saidbody and aligned with said central longitudinal axis, and a housingcontaining said body.

6. A jet perforating charge as set forth in claim 5, and a metallicliner in the recess and conforming thereto.

7. A jet perforating charge as set forth in claim 6 wherein saiddihedral angle is within the range of 85 to 95.

7 8 8. A jet perforating charge as set forth in claim 6 PATENTS whereinthe thickness of said liner is within the range of 023 France Jan 714953 0.04 to 0.08 inch. ""TT t 7 OTHER REFERENCES References Cited inthe me of this P I 5 Publication by M. Suhharensky, entitled PhenomenaUNITED STATES PATENTS V I Produced by the Explosion ofHollow Cartridgesand the Practical Importance of the Application of the Principle2,399,211 Davis P 9 of Hollow Cartridges and Charges in BlastingPractice, 2,407,093 Mohaupt Septu3, 1946 Y translation from RussianVoina i Teknka, 253 (1926), 2,629,325 Sweetrnan Feb. 24, 1953 10 18-24,8 sheets drawing. Two sheets drawing contain-' 2,667,836 Church et a1.Feb. 2, 1954 ing FIGS. 241027 and 30 to 35 considered pertinent.2,708,408 7 Sweetman May 17, 1955 (Copy in Class 102H.C. Division 10.)

